1. Field of the Invention
The present invention relates to high frequency circuit modules including variable matching circuits configured to perform impedance matching for antennas.
2. Description of the Related Art
Currently, various wireless communication devices are in practical use. These wireless communication devices are typically equipped with high frequency circuit modules that enable communications at a plurality of different kinds of frequency bands. Such a high frequency circuit module that enables communications at a plurality of different kinds of frequency bands includes an antenna capable of transmitting and receiving radio signals across a wide frequency range and a front-end circuit module capable of performing transmission processing and reception processing of communication signals at the plural kinds of frequency bands.
In this high frequency circuit module, it is necessary to have a matching circuit for performing impedance matching between the antenna and the front-end circuit, and the matching circuit is connected between the antenna and the front-end circuit.
Further, to perform the impedance matching across the wide frequency range as described above, a variable matching circuit such as, for example, the one illustrated in Japanese Unexamined Patent Application Publication No. 2012-515482, may be used. FIG. 10 is a circuit diagram of a variable matching circuit in a related art.
As illustrated in FIG. 10, a high frequency circuit module 10PR including a variable matching circuit described in Japanese Unexamined Patent Application Publication No. 2012-515482 includes an antenna port PANT for connecting an antenna ANT and a front-end port PRF for connecting a transceiver circuit 90. A variable capacitor 311PR is connected between the antenna port PANT and the front-end port PRF. An inductor 200PR is connected between the antenna port PANT and ground. A parallel circuit of an inductor 340PR and a variable capacitor 312PR is connected between the front-end port PRF and the ground.
The impedance matching at the plural frequency bands is achieved by varying capacitances of the variable capacitors 311PR and 312PR of this variable matching circuit.
As illustrated in FIG. 10, in many cases in the related art, the variable matching circuits for antenna impedance matching include the inductor between the antenna port PANT and the ground.
However, such a variable matching circuit including an inductor connected between the antenna port PANT and the ground as the one described above has a limited adjustable impedance range because of including that inductance.
This poses an issue of higher transmission loss in some of the frequency bands (that prevents accurate impedance matching) when the impedance matching is performed for respective ones of the plural kinds of frequency bands existing across a wide frequency range.
On the other hand, the inductor is an effective device since it facilitates coarse matching between the antenna and the front-end as well as functions as an ESD device.